// This line is a trick to initialize the AudioContext

// that will work on all recent browsers

var ctx = window.AudioContext || window.webkitAudioContext;

var audioContext;

var gainExample, gainSlider, gainNode;

​

window.onload = function() {

   // get the AudioContext

   audioContext = new ctx();

​

   // the audio element

   gainExample = document.querySelector('#gainExample');

   gainSlider = document.querySelector('#gainSlider');

​

   // fix for autoplay policy

  gainExample.addEventListener('play',() => audioContext.resume());

  buildAudioGraph();

  // input listener on the gain slider

  gainSlider.oninput = function(evt){

    gainNode.gain.value = evt.target.value;

  }; 

};

​

function buildAudioGraph() {

    // create source and gain node

    var gainMediaElementSource = audioContext.createMediaElementSource(gainExample);

    gainNode = audioContext.createGain();

    // connect nodes together

    gainMediaElementSource.connect(gainNode);

    gainNode.connect(audioContext.destination);

​

​

}

​

​